Department of Biochemistry, University of Nigeria, Nsukka, Nigeria.
Cell Biochem Biophys. 2011 Dec;61(3):573-84. doi: 10.1007/s12013-011-9239-8.
We investigate the conformational differences between HbA and HbS in the presence and absence of Ca(2+) concentrations (0-40 μM) akin to those within the erythrocyte cytoplasm and the membrane mimetic and native structure disrupting environments of the Plasmodium parasite food vacuole at pH 5.0. The experiments were monitored by UV-Vis spectrophotometery in the range of 250-650 nm. Our results suggest that the HbS, on interacting with both the membrane mimic and 40 μM Ca(2+), undergoes an "expansion" akin to the burst phase of proteins accompanied by tyrosine exposure while that of the HbA occurred with tryptophan exposure. Our results suggest conformational flexibility in the HbS unlike in the HbA. Besides, the spectral results also suggest that the HbS complexes with the Ca(2+) in its immediate environment without strain (due to its inherent conformational flexibility), unlike the HbA, thus appropriating the cation from its vicinity. The implications of these results are discussed in the light of possible mechanisms employed by the HbS to resist protease digestion or at least slow down the kinetics of the protease activities and on how these same factors can predispose the homozygous HbS individuals to sickling and consequent vaso-occlusive crisis.
我们研究了在类似于红细胞细胞质内的 Ca(2+)浓度（0-40 μM）以及疟原虫食物泡的膜模拟物和天然结构破坏环境存在和不存在 Ca(2+)的情况下，HbA 和 HbS 之间的构象差异。实验通过在 250-650nm 范围内的紫外-可见分光光度法进行监测。我们的结果表明，在与膜模拟物和 40μM Ca(2+)相互作用时，HbS 经历了一种“扩张”，类似于蛋白质的爆发阶段，伴随着酪氨酸暴露，而 HbS 的则伴随着色氨酸暴露。我们的结果表明，HbS 比 HbS 具有构象灵活性。此外，光谱结果还表明，HbS 与其周围环境中的 Ca(2+)结合而没有应变（由于其固有构象灵活性），而 HbS 则不然，因此从其附近获取阳离子。根据 HbS 抵抗蛋白酶消化或至少减缓蛋白酶活性动力学的可能机制以及这些相同因素如何使纯合 HbS 个体易患镰状细胞病和随后的血管阻塞性危机，讨论了这些结果的意义。
